1. Field of the Invention
The present invention relates to an air dehumidifying apparatus for dehumidifying damp air, and more particularly to an air dehumidifying apparatus used for dehumidifying compressed air for marine control equipment.
2. Description of the Related Art
There are known various types of air dehumidifying apparatus, and in marine use, for example, the air dehumidifying apparatus of refrigerating and reheating type has been mainly employed hitherto. The air dehumidifying apparatus of refrigerating and reheating type is an air dehumidifying apparatus of a type of separating steam from damp air by condensing the steam contained in the damp air, and has such advantages as stable performance and easy operation. As a refrigerant contained in the refrigerating machine used in the air dehumidifying apparatus of this refrigerating and reheating type are used generally, chlorofluorocarbons (CFCs) such as R-12 (CCl.sub.2 F.sub.2) and hydrochlorofluorocarbons (HCFCs) such as R-22 (CHClF.sub.2), and the manufacture of such CFCs has been already prohibited or limited by international treaty or is to be prohibited or limited shortly. Therefore, it will not be permissible to supply CFCS as the refrigerant stably and continuously in future, and it is predicted that it will be difficult to employ the air dehumidifying apparatus of refrigerating and reheating type using such conventional CFCs as the refrigerant. On the other hand, the refrigerants out of the scope of such international treaty and the refrigerating machines using such refrigerants are still in the developmental stage, and not are not in practical use.
As the air dehumidifying apparatus, meanwhile, other types are also known, such as the silica gel type and seawater cooling type. The air dehumidifying apparatus of the silica gel type is an air dehumidifying apparatus of a type of adsorbing and removing moisture from damp air by the capillary phenomenon by using silica gel, and it comprises two adsorption towers containing silica gel, and is operated in a specific cycle so that each adsorption tower may adsorb and release moisture alternately. Due to the necessity of two adsorption towers, such apparatus has a problem that the apparatus is increased in size. The air dehumidifying apparatus of the seawater cooling type is an air dehumidifying apparatus of a type which separates steam from air by cooling damp air by seawater and condensing the steam contained in the damp air. This process, however, has a problem of low performance because the damp air cannot be cooled to a temperature lower than the temperature of the seawater.
Further, regarding an air dehumidifying apparatus of another type, recently, attention is being given to an air dehumidifying apparatus having a high performance by utilizing a separation membrane having a property of separating steam in air. However, the damp air to be dehumidified, for example, compressed air boosted by an air compressor contains oil, dust or foreign matter, and when foreign matter gets into the separation membrane, it clogs the fine passage in the membrane for passing damp air, and shortens the service life of the separation membrane. In marine use, in particular, it is more difficult to supply and repair parts than in land use such as in a factory or the like, and therefore the air dehumidifying apparatus of separation membrane type was not widely installed because of a strong demand for service life and reliability of parts of the apparatus. Alternatively, although it is also attempted to use a filter for the purpose of extending the life of the separation membrane, there is a problem that the filter life is short.
Conventionally, moreover, in the air dehumidifying apparatus of separation membrane type, the container accommodating the separation membrane for composing the air dehumidifying apparatus, filters, pipes, and valves are composed independently, and they are arranged and connected by piping at the site of installation of the air dehumidifying apparatus to complete the air dehumidifying apparatus. Therefore, the apparatus is larger in size, and especially in marine use, the work load increases in the poor working environments found in a ship. In the ship, and in a small ship in particular, although there is a small space for installing machines such an as air dehumidifying apparatus, such air dehumidifying apparatus of the separation membrane type requires a wide space for installation.